A thermosensitive recording medium is obtained by grinding a colorless or pale colored basic leuco dye (henceforth referred to as “dye”) and an electron accepting color developing agent (henceforth referred to as “color developing agent”) each into fine particles, preparing dispersions, blending the dispersions, preparing a coating solution by adding a binder, a filler, a sensitivity improving agent, a lubricant and other aids and applying the coating solution on a support material such as paper, synthetic paper, film, plastic and the like. The color is developed instantaneously through a chemical reaction when heated using a thermal head, hot stamp, thermal pen, laser beam and the like to yield a recorded image. The thermosensitive recording medium is being used extensively in facsimiles, terminal printers of computers, automatic ticket vending machines, measurement recorders and the like. As the thermosensitive recording medium becomes to be used in various applications, higher level of image stability and stability in white part against water, oil, plasticizer, solvent and the like are required. When a mobile type printer is used outdoors, sticking resistance is especially required. Sticking resistance is referred as a property resistant to a problem, that is, an outer surface of a thermosensitive recording medium is heated by a printer and sticks to the printer head, in which some part of the thermosensitive recording medium is not printed. As the quality of thermal printing becomes high recently, in which, the printing precision is more than 200 dpi or the printing speed is more than 100 mm/sec, a thermosensitive recording medium suitable for these new applications is demanded.
It is well known to install a protective layer on a thermosensitive recording layer in order to improve a storage stability of a thermosensitive recording medium. It is also commonly conducted to have the protective layer contain a polyvinyl alcohol to improve membrane strength or an acrylic resin to improve water resistance and chemical resistance (References 1, 2 etc.). However, while a hydrophobic resin emulsion, such as acrylic emulsion, is used in a protective layer to improving water resistance of a thermosensitive recording medium (Reference 3), printing run-ability, such as sticking resistance, becomes worse because of insufficient heat resistance of the acrylic emulsion. And it is conducted to have a protective layer contain various inorganic pigments, such as kaoline, in order to improve printing run-ability (Reference 4).    Reference 1: Japanese Patent Application Public Disclosure H11-314454    Reference 2: International Publication WO2007/049621    Reference 3: Japanese Patent Application Public Disclosure H01-196389    Reference 4: Japanese Patent No. 3971453